Vibration damping mechanism



Feb. 6, 1962 J. R. WARREN 3,020,006

VIBRATION DAMPING MECHANISM Original Filed Dec. 6, 1954 INVENTOR. JAMESR. WARREN ATTORNEYS United States atent 3,020,006 VIBRATION DAMPIN GMECHANISM James R. Warren, Washington, D.C., assignor to the UnitedStates of America as represented by the Secretary of the NavyOriginalapplication Dec. 6, 1954, Ser. No. 473,490, new Patent No.2,996,627, dated Aug. 15, 1961. Divided andthis. application Mar. 21,1957, Ser. No. 651,567 3 Claims. -(Cl..244-75) This invention relates toan oscillation damping mecha nism and more particularly to a mechanismfor damping wing oscillations of airborne missiles. This application isa division of copending US. patent application Serial No. 473,490, filedDecember 6, 1954, by the same inventor, now Patent No. 2,996,267, Aug.15, 1961.

It is generally the practice. in the guided missile area to provide winglocks for locking'the wings of a missile in a fix'ed'position duringlaunching-and prior to the advent of guidance control. At the specifiedtime, when it is desired to regulate the coure of the missile, the winglocks retract and the servo-control mechanism of the guidance systemassumes command of the wings.

However, in order to protect the servo-control mechanism fromself-inflicted damage in operating against the wing locks, there isprovided a time interval between wing lock retraction and the advent ofguidance control. During this period of time the wing is free of anycontrol whatsoever and is especially subject to regenerativeoscillations. At the ultra-high speeds experienced by airborne guidedmissiles these regenerative oscillations reach destructive proportionsand it is to be this cause that wing failures in guided missiles havebeen attributed.

The principal object of the present invention is to correct thisdisadvantageous situation by providing a damp ing machanism which willlimit the oscillatory movements of a missile wing.

It is another object of the invention to provide a damping mechanism,the damping action of which may be varied to selectively eliminate onlythose oscillations thought to be damaging to the structural parts of themissile wing.

Still further objects and advantageous aspects of the invention willbecome apparent from the following detailed description taken inconjunction with the accompanying drawings, and in which:

FIG. 1 is a diagrammatic view of one embodiment of the inventionillustrating the arrangement of the elements of the damping mechanism inrelation to the missile wing; and

FIG. 2 is a diagrammatic view of a second embodiment of the inventionsimilarly illustrating the arrangement of the elements of the dampingmechanism in relation to the missile wing.

Broadly, the invention includes a dashpot mechanism, the movable memberof which is connected to the wing by a mechanical linkage so thatoscillatory movements of the wing may be controlled by the movablemember. Movement of this movable member is resisted by a fluid, theviscosity of which is variable. By varying the viscosity of the fluidthe mobility of the movable member is varied. A viscosity is chosenwhich will prevent extreme and rapid movements of the movable member andhence oscillations which will damage the structural parts of the wing.

Referring now to FIG. 1, there is shown a missile wing 12 which isconnectable to the body of the missile by a stub shaft 10. Shaft alsoserves to control the attitude of the wing 12 with respect to themissile body.

An end instrument 11, of the type commonly used in the telemeteringphase of the guided missile art to measure angular displacement, isoperatively connected to the stub shaft 10 to receive movements of theshaft.

The end instrument 11 is also conventionally known as an angularposition indicator or a motion meter and, gen

erally, comprises a threaded shaft which, when rotated, moves a magneticshunt in the field of a control coil constituting the inductive elementof an oscillator. As the magnet shunt moves, the effective inductance ofthe con trol coil and hence the frequency of the oscillator, changes.

The output of the end instrument 11, i.e. the output of the oscillatorthereof, is transmitted to a frequency selector 13 the output of whichis fed into a detector 14. The frequency selector 13 passes only thosesignals having frequencies indicative of those vibrations considereddamaging to the wing 12. Suitable amplification of the selected signalsis also provided in the frequency selector A coil 15 surrounding ahydraulic cylinder 16 containing a magnetic fluid e.g. a mixture of oiland iron filings, is connected to the output of the detector 14. .Apiston, slidably mounted within the cylinder 16, is connected by apiston rod 17 and a suitable mechanical linkage 18 consisting ofelements 19 and 20 to the stub shaft 10 so that movements of shaft 10and thus the wing 12 may be controlled by the movements of the piston17.

In operation, movements of the wing 12 are transmitted through the stubshaft 10 to the mechanical linkage 18, to the piston rod 17 andultimately to the piston in cylinder 16 which is restrained in movementby the magnetic mixture in the cylinder 16. Conversely, it is understoodthat a restraint on the movement of the piston in cylinder 20constitutes a resistance to the movement of the wing 12.

Thus, it can be seen that the degree of movement of the wing 12determines the degree of resistance offered by the fluid mixture to arecurrent movement of the wing 12. Therefore, vibrations of theregenerative type are effectively damped.

The mechanism exerts this stabilizing effect during the entire flight tothe missile and only those vibrations considered to be damaging to thestructural parts of the wing are clamped.

Turning now to the second embodiment of the invention as illustrated inFIG. 2, the pistonrod 17, slidably connected tothe piston mounted withinthe cylinder 16 filled with a mixture of oil and iron filings, isconnected by means of the mechanical linkage 18 to the wing 12, throughthe stub shaft 10. As in the first embodiment of the invention, themovements of the wing 12 are controllable through the mechanical linkage18 by the movements of the piston in cylinder 16. Coil 15 surrounds thecylinder 16 as in the previously described embodiment of the inventionillustrated in FIG. 1, and it is connected in parallel with a capacitor26, a leak resistance 27, and a servo switch 28; and in series with alimiting resistance 29 to a source of direct current electricity 31 byleads 32 and 33.

The current passing through the coil 15 of FIG. 2 determines thestrength of the magnetic field produced within the cylinder 16 andhence, the viscosity of the fluid mixture. The source of electricity 31,the limiting resistance 29, and the leak resistance 27 are appropriatelychosen to provide a constant current through the coil which determines aviscosity suflicient to dampen those vibrations considered to bedamaging to the structural parts of the wing 12.

Prior to launching of the missile the servo switch 28 is closed, thusenergizing the coil 15, of FIG. 2. With the advent of guidance systemcontrol, the servo switch 28 is opened to electrically disconnect thesource of electricity 31 from the remainder of the circuit. The chargeon the capacitor 26 then decays to supply energizing current through thecoil 15, of FIG. 2. This pro vides a smooth transition to guidancesystem control.

In this manner the damping influence exerted by the mechanism upon thewing 12 continues until some time after the advent of guidance systemcontrol when the capacitor 26 has released its charge. After the chargeon the capacitor 26 has been exhausted, the damping mechanism has noeffect on the movemens of the wing 12.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

What is claimed is:

1. In a vibration damping mechanism for use in damping wing oscillationsof airborne missiles, the combination of, a container, a mixture ofviscous substance and a magnetizable substance substantially fillingsaid container throughout, a piston slidably mounted within saidcontainer and connected to the missile wing through a mechanical linkageso that wing vibrations are controlled by the movements of said piston,a magnetizing coil surrounding said container and energized by anelectrical circuit including a vibration sensing instrument measuringwing vibrations and producing electrical signals representative of thewing vibrations, an amplifier amplifying said electrical signals, and adetector rectifying said electrical signals, whereby said rectifiedelectrical signals energize said coil to produce a varying magneticfield within said container.

2. An arrangement as recited in claim 1, wherein said vibration sensinginstrument is mechanically associated with said wing.

3. An arrangement as recited in claim 2, and a filter connected to theoutput of said vibration sensing instrument.

References Cited in the file of this patent UNITED STATES PATENTS2,361,071 Vang Oct. 24, 1944 2,667,237 Rabinow Jan. 26, 1954 FOREIGNPATENTS 747,147 Germany Jan. 8, 1945

